High alumina ceramic insulator compositions

ABSTRACT

A high alumina ceramic composition having improved thermal and mechanical properties consists of 80 to 98 percent by weight of alumina of a main constituent and 2 to 20 percent by weight of an accessory constituent, which consists of a mixture of SiO2, B2O3 and at least one oxide (RO) selected from the group consisting of alkaline earth metal oxides and bivalent metal oxides, said mixture having a composition range encircled with points A, B, C and D in a triangular coordinate.

Asano et al.

HIGH ALUMINA CERAMIC INSULATOR COMPOSITIONS Inventors: Toshiyasu Asano; Kazuyoshi Sumi, both of Nagoya, Japan Assignee: NGK Spark Plug Co., Ltd., Nagoya,

Japan Continuation of Ser. No. 324,153, Jan. 16, 1973, I abandoned. 6

Foreign Application Priority Data Jan. 21, 1972 Japan 47-8657 'U.S. Cl 106/46; lO6/73.4

1m. c1. 1. c0413 33/26 Field 61 Search 106/73.4, 46

References Cited UNITED STATES PATENTS 3/1914 Locke 106 46 1 1 Dec. 30, 1975 1,091,679 3/1914 Locke 106/46 1,120,951 12/1914 Locke 106/46 2,760,875 8/1956 Schwartzwalder. 106/46 3,019,116 1/1962 Doucette 1. 106/46 3,141,786 7/1964 Bugosh 106 73.4 3,167,438 1/1965 Bristow 106/46 3,627,547 12/1971 Bailey 106/46 Primary Examiner-Winst0n A. Douglas Assistant Examiner-Mark Bell Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher 57 ABSTRACT A high alumina ceramic composition having improved thermal and mechanical properties consists of 80 to 98 percent by weight of alumina of a main constituent and 2 to 20 percent by weight of an accessory constituent, which consists of a mixture of SiO B 0 and at least one oxide (R0) selected from the group consisting of alkaline earth metal oxides and bivalent metal oxides, said mixture having a composition range encircled with points A, B, C and D in a triangular coordimate.

1 Claim, 1 Drawing Figure US. Patent Dec. 30, 1975 3,929,96

0 /0 I00 90 W B205 HIGH ALUMINA CERAMIC INSULATOR COMPOSITIONS used as various high-temperature electric insulating materials because they are high in the mechanical strength, thermal properties and high-temperature insulation resistance and are excellent in the chemical stability. However, when they are used as an insulating body for spark plugs under a severe condition, they are particularly required to have higher mechanical strength and thermal shock resistance.

An object of the present invention is to satisfy the above-described requirements so as to further-improve thermal and mechanical properties in the high alumina ceramics.

The present invention provides a high alumina ceramic-composition which consists of 80 to 98 percent by weight of alumina of a main constituent and 2 to 20 percent by weight of an accessory constituent consisting of a mixture of SiO B 0 and at least one oxide (R0) selected from the group consisting of alkaline earth metal oxides of CaO, MgO, BaO, SrO and BeO and bivalent metal oxides of NiO, CdO, ZnO, MnO, CrO and SnO, said mixture having the following composition range encircled with the points A, B, C and D in the triangular coordinate:

When the amount of alumina is less than 80 percent by weight, the apparent specific gravity, flexural strength and thermal shock resistance are poor, while 2 when the amount of alumina is more than 98 percent by weight, the firing temperature excessively rises and the mass production is not suitable.

The reason why the amount of the accessory constituent is limited to the composition range encircled with the points A, B, C and D in the triangular coordinate i as follows:

When the amount of B 0 is greater than the above composition range, the firing temperature excessively rises and the variance of the properties of the resulting products becomes large, while when the amount of B 0 is less than the above composition range, the strength of the products is insufficient. Furthermore, it has experimentally been found that a good result is not obtained when the amounts of SiO and R0 are beyond the above composition range.

The following example is given in illustration of this invention and is not intended as limitations thereof.-

EXAMPLE consisting of a mixture of SiO alkaline earth metal oxides of MgO and CaO, and a boron compound, which is converted to B 0 by firing, in various composition ranges as shown in the following Table l, and the resulting mixture was granulated by spray-drying to obtain granules having a grain size of 30 to 250p These granules were pressed at a pressure of 500 Kglcm and the resulting shaped specimen was heated in a gas-fired kiln to 1,300C. Thereafter, the temperature was raised at a rate of 70C per hour, while the shaped specimen was taken out at intervals of 20C during the heating and the fired state was inspected with a fuchsin solution. By such an inspection the temperature was raised up to the point that the stains do not occur, and the firing was completed. The apparent specific gravity,

0 flexural strength and thermal shock resistance were measured with respect to the samples to obtain a result as shown in Table 1.

Table 1 Composition of accessory constituent (Wt.%)

Main cons- Characteristic value Metal oxides (R0) Firing Thermal Samtituent Accessory temper- Apparent Flexural shock ple Ago, constituent ature specific strength resistance No. (Wt.%) (Wt.%) SiO, B O CaO MgO Total ("C) gravity (Kg/cm)X10 '(C) Remarks 1 94.0 6.0 28.0 60.0 8.0 4.0 12.0 1,630 3.59 4.1 740 PointA of FIG. 1 2 36.0 60.0 2.7 1.3 4.0 1,640 3.58 3.9 700 Point B of FIG. 1 3 89.0 1.0 6.7 3.3 10.0 1,600 3.67 3.8 760 Point C of FIG. 1 4 69.0 1.0 20.0 10.0 30.0 1,550 3.67 4.0 760 Point D of FIG. 1 5 32.0 60.0 5.3 2.7 8.0 1,630 3.58 4.2 730 6 54.0 40.0 4.0 2.0 6.0 1,610 3.60 4.5 710 7 72.0 20.0 5.3 2.7 8.0 1,600 3.65 4.1 760 8 79.5 1.0 13.0 6.5 19.5 1,540 3.68 4.3 790 9 56.0 20.0 16.0 8.0 24.0 1,540 3.67 4.3 750 10 42.0 40.0 12.0 6.0 18.0 1,490 3.63 4.1 770 11 48.0 40.0 8.0 4.0 12.0 1,550 3.61 4.8 780 I2 64.0 20.0 10.7 5.3 16.0 1,560 3.66 4.7 .770 13 94.0 6.0 27.5 57.5 10.0 5.0 15.0 1,600 3.60 3.4 690 Beyond 14 30.0 62.5 5.0 2.5 7.5 1,650 3.57 3.5 690 the scope 15 40.0 57.5 1.7 0.8 2.5 1,640 3.58 3.2 670 of the 16 90.0 5.0 3.3 1.7 5.0 1,650 3.67 2.8 650 present 17 79.5 0.5 13.3 6.7 20.0 1,540 3.68 3.3 680 invention Table l-continued Composition of accessory constituent (Wt.%)

. Main cons Metal oxides (RO) Characteristic value Firing Thermal Samv tttuent Accessory temper- Apparent Flexural a shock ple A1 constituent ature specific strength resistance No. (Wt.%) (Wt.%) SiO B 0 CaO MgO 5 Total ("C)- gravity (Kg/cm )Xl0'* (C) Remarks Note) Test for flexural strength The flexural strength was measured with respect to a sample of 50mm 100mnt 4mm by means of a Michaelis' tester. Test for thermal shock resistance A sample of 70mm 10mmX6mm at room temperature was dipped in a bath of tin melted to 600C by an electric furnace for 3 seconds,

andthen taken out therefrom and cooled in air. The cooled r was test there are g and cracks or not. lf no finding, the bath temperature was raised at a rate of 509C and the said inspection was repeated. The thermal shock resistance was expressed as an average temperature when the damages and cracks occurred in samples.

sition range encircled with the points A, B, C and D in the triangular coordinate are excellent in the flexural strength and,.thermal .shock resistance as compared ,withthe sample Nos. 13 to 18 containing the accessory constituent beyond the above described composition range, and particularly the sample Nos. 1 1 and.12 plotted on the line bonded to each center point Nos. 5 and 8 of. lines A-B and C-D have a remarkable effect.

Then, the same test as described above was made with respect to samples prepared according to the sample No- 12 wherein the accessory constituent consisted of 64 percentby weight of SiO 20 percent by weight of. B 0 and 16 percent by weightof the metal oxide ROselected from the group consisting of CaO, MgO, ZnO and a combination with other oxide thereof. The

obtained results are shown in the following Table 2.

As seenfrom Table 2, the sample Nos. 12a-12v consisting of 94 percent by weight of the main constituent A1 0 and 6 percent by weight of the accessory constituent which is a combination of 64 percent by weight of SiO 20.percent byweight of B 0 and 16 percent by weight of R0 have satisfactory characteristic values in the firing temperature, apparent specific gravity, flexural strength-and thermal shock resistance which are substantially'equal to those of Table 1. However, the sample Nos. 18a and 18b prepared by changing the composition of the accessory constituent in the control sample No. 18 cannot attain the given effect, and also the sample No. 14a corresponding to the sample No. 14 is difficult tov be fired. Y

Moreover, the same test as described above was made with respect to samples obtained, by varying the mixing ratio of the main constituent A1 0 and the accessory constituent having the composition range of SiO R0 and B 0 corresponding to those of the sample Nos. 5-, 8, 11 and 12' of Table 1. The obtained results are shown in the following Table 3.

Table 2 Composition of accessory constituent Characteristic value Metal oxides (R0) v Ther- Main Acce- Appamal' constissory rent Flexural shock Samtuent consti- Other Firing Specistrength resisple A1,0, tuent oxi- Temp. fic gr- (Kg/cm) tance No. (Wt.%) v(Wt.%) SiO, B 0 CaO MgO ZnO.. des Total (?C) .avity. X10 7 (C), Remarks 12a 94.0 6.0 64.0 20.0 16.0 16.0 1,600 3.63 3.8 750 12b 8.0 8.0 1,550 3.65 4.2 780 12c 4.0 SnO 4.0 1,530 3.64 5.0 805 12d 13210 8.0 1,630 3.68 3.9 770 12c 8.0 1,620 3.67 4.7 740 12f CdO 8.0 1,650 3.65 3.8 V 730 12g v v 1 N10 8.0 1,590 3.67 i 4.2 760 12h MnO 8.0 1,600 3.66 3.8 760- l2i 1 SrO 8.0 1,590 3.64 3.6 810 12j 4.0 SrO 4.0 1,650 3.64 3.7 750 12k BeO 8.0 1,630 3.67 4.0 750 121 SnO 8.0 1,680 3.68 4.0 708 12m 16.0 1,500 3.66 4.7 780 12n 8.0 SrO 8.0 1,530 3.66 4.7 790 BaO 8.0 1,530 3.68 4.5 770 12p 8.0 1,570 3.61 4.1 750 l2q M0 8.0 1,600 3.62 4.0 750 12r 16.0 1,700 3.56 3.8 710 12s 8.0 Ba0'8.0 1,690 3.60 3.8 710 l2t SrO 8.0 1,670 3.57 4.0 740 12u M0 8.0 1,670 3.60 3.6 700 12v MnO 8.0 1,620 3.66 4.5 740 Beyond 14a 94.0 6.0 30.0 62.5 3.8 3.7 7.5 above the 7 1,720 scope 18a v 62.5 5.0 16.3 16.2 32.5 1,610 3.66 3.7 650 of the 18b SrO 16.2 32.5 1,590 3.65 3.2 690 present invention Table 3 Compositionof accessory Characteristic value constituent (Wt.%)

Metal oxides Main Acce- Appaconsttssory rent Flexural Samtuent consti- Firing speci strength Thermal ple A1 0 tuent Temp. fic gr- (Kg/cm) shock No. (Wt.%) (Wt.%) SiO B 0 CaO MgO Total (C) avity X resis- Remarks tance 5a 75.0 25.0 32.0 60.0 5.3 2.7 8.0 1,410 2.8 1.9 560 Beyond 8a 79.5 1.0 13.0 6.5 19.5 1,420 3.1 2.2 600 the scope lla' 48.0 40.0 8.0 4.0 12.0 1,390 2.9 2.6 610 of the I present 12a 64.0 20.0 10.7 5.3 16.0 14,000 3.0 2.4 600 invention 5b 80.0 20.0, 32.0 60.0 5.3 2.7 8.0 1,460 2.9 2.6 620 8b 79.5 1.0 13.0 6.5 19.5 1,430 3.2 2.7 660 11b 48.0 40.0 8.0 4.0 12.0 1,410 3.0 3.0 660 12b 64.0 20.0 10.7 5.3 16.0 1,430 3.1 3.0 670 5c 85.0 15.0 32.0 60.0 5.3 2.7 8.0 1,510 3.1 2.9 650 8c 79.5 1.0 13.0 6.5 19.5 1,480 3.4 3.1 690 11c 48.0 40.0 8.0 4.0 12.0 1,440 3.3 3.4 700 12c 64.0 20.0 10.7 5.3 16.0 1,460 3.3 3.5 690 5d 90.0 10.0 32.0 60.0 5.3 2.7 8.0 1,560 3.4 3.4 700 8d 79.5 1.0 13.0 6.5 19.5 1,500 3.5 3.8 760 11d 48.0 40.0 8.0 4.0 12.0 1,490 3.4 4.0 740 12d 64.0 20.0 10.7 5.3 16.0 1,480 3.5 4.1 740 5 94.0 6.0 32.0 60.0 5.3 2.7 8.0 1,630 3.6 4.2 730 8 79.5 1.0 13.0 6.5 19.5 1,540 3.7 4.3 790 11 48.0 40.0 8.0 4.0 12.5 1,550 3.6 4.8 '780 12 64.0 20.0 10.7 5.3 16.0 1,560 3.7 4.7 770 5e 98.0 2.0 32.5 60.0 5.3 2.7 8.0 1,700 3.8 3.5 660 8e 79.5 1.0 13.0 6.5 19.5 1,640 3.8 3.7 690 1 1e 48.0 40.0 8.0 4.0 12.5 1,660 3.8 4.2 720 12a 64.0 20.0 10.7 5.3 16.0 1,680 3.8 4.0 700 above Beyond 5f 99.0 1.0 32.5 60.0 5.3 2.7 8.0

1,710 the 8f 79.5 1.0 13.0 6.5 19.5 1,710 3.8 2.9 640 scope above of llf' 48.0 40.0 8.0 4.0 12.5

1,710 the above present 12f 54.0 20.0 10.7 5.3 16.0

1,610 invention As seen from Table 3, the compositions consisting of 40 80 to 98 percent by weight of alumina and 2 to percent by weight of the accessory constituent (sample Nos. 5b'-12b' to 5el2e') have the substantially same characteristic values as those of the sample Nos. 5-12 of Table 1. On the other hand, the compositions consisting of 75 percent by weight of alumina and percent by weight of the accessory constituent (sample Nos. 5a-12a) are low in the apparent specific gravity, flexural strength and thermal shock resistance, while in case of the compositions consisting of 99 percent by weight of alumina and 1 percent by weight of the accessory constituent (sample Nos. 5f-l2f) the firing temperature excessively rises and the mass production is not suitable.

FIG. 1 is a triangular coordinate showing a composition range of three component system, i.e., SiO B 0 and at least one oxide (R0) selected from the group consisting of alkaline earth metal oxides of CaO, MgO, BaO, SrO and BeO and bivalent metal oxides of NiO, CdO, ZnO, MnO, CrO and SnO, which constitutes the accessory constituent of the high alumina ceramic composition according to the present invention.

As seen from the above Tables 1, 2 and 3, the high alumina ceramic compositions of the present invention consisting of 80 to 98 percent by weight of the main constituent A1 0 and 2 to 20 percent by weight of the accessory constituent consisting of a mixture of SiO B 0 and at least one oxide RO having the composition range encircled with the points A, B, C and D in the triangular coordinate have an excellent effect of improving mechanical strength, flexural strength and thermal shock resistance required for the manufacture of high-temperature electric insulating materials without raising the firing temperature.

According to the present invention, the reason why at least one oxide RO is selected from the group consisting of alkaline earth metal oxides of CaO, MgO, BaO, S10 and BeO and bivalent metal oxides of NiO, CdO, ZnO, MnO, CrO and SnO is based on the experimental results. That is, it is well-known that in the alumina ceramics, aluminosilicate glass as a main component of grain boundary has a higher thermal expansion coefficient than that of alumina grains, but borosilicate glass added with B 0 becomes smaller in the thermal expansion coefficient. Therefore, the inventors have considered that when such a borosilicate glass is added with a network modifier having a large ionic radius and a small electric charge, the thermal expansion coefficient will be further lowered and the thermal shock resistance will be increased. For this purpose, an experiment was made with respect to MgO having an ionic radius/valence ratio of 0.39 and CaO having an ionic radius/valence ratio of 0.53 and the results shown in Table l were obtained. Further, when the experiment was made with respect to the other alkaline earth metal oxides and further to bivalent metal oxides having an approximately equal ionic radius/valence ratio which do not cause considerable coloration to fired body nor degrade insulation resistance, the desired 7 results were obtained.

Moreover, as the network modifier there are alkali metal ions such as K, Na, Li and the like, but these ions considerably degrade the insulation resistance, so that they cannot be used as the accessory constituent of the present invention.

For the reference, ionic radii and valences of alkaline earth metals and bivalent metals are shown in the following Table 4.

In the metal oxide expressed by R0, metals such as Ni, Mn, etc. capable of forming trivalent or polyvalent 8 oxides are included, but when these oxides other than bivalent oxide are used, they may be calculated as bivalent oxide.

What is claimed is: 1. An alumina ceramic insulator for use in a spark plug, formed by sintering at a temperature of 14 l 0C to 1700C a mixture of to 98 percent by weight of alumina of a main constituent and 2 to 20 percent by weight of flux material of an accessory constituent consisting of SiO,, B 0 and'at least one oxide (R0) selected from the group consisting of alkaline earth metal oxides of CaO, MgO, BaO, SrO and BeO and bivalent metal oxides of MO, CdO, ZnO, MnO, CrO and SnO, said-flux material having the following composition range encircled with the points A, B, C and D in the triangular coordinate: 

1. AN ALUMINA CERAMIC INSULATOR FOR USE IN A SPARK PLUG, FORMED BY SINTERING AT A TEMPERATURE OF 1410*C TO 1700*C A MIXTURE OF 80 TO 98 PERCENT BY WEIGHT OF ALUMINA OF A MAIN CONSTITUENT AND 2 TO 20 PERCENT BY WEIGHT OF FLUX MATERIAL OF AN ACESSORY CONSTITUENT CONSISTING OF SIO2, B2O3 AND AT LEAST ONE OXIDE (RO) SELECTED FROM THE GROUP CONSISTING OF ALKALINE EARTH METAL OXIDES OF CAO, MGO, BAO, SRO AND BEO AND BIVALENT METAL OXIDES OF NIO CDO, ZNO, MNO, CRO AND SNO, SAID FLUX MATERIAL HAVING THE FOLLOWING COMPOSITION RANGE ENCIRCLED WITH THE POINTS A, B, C AND D IN THE TRIANGULAR COORDINATE: 